Bone grafts

ABSTRACT

Spinal spacers  20  are provided for fusion of a motion segment. The spacers include a load bearing member  21  having a wall  22  sized for engagement within a space between adjacent vertebrae to maintain the space and an effective amount of an osteogenic composition to stimulate osteoinduction. The osteogenic composition includes a substantially pure osteogenic factor in a pharmaceutically acceptable carrier. In one embodiment the load bearing member includes a bone graft impregnated in an osteogenic composition. In another embodiment, the osteogenic composition  30  is packed within a chamber  25  defined in the graft. Any suitable configuration of a bone graft is contemplated, including bone dowels, D-shaped spacers and cortical rings.

This application is a Divisional of U.S. application Ser. No.08/740,031, filed Oct. 23, 1996, now abandoned.

FIELD OF THE INVENTION

The present invention relates to spacers, compositions, instruments andmethods for arthrodesis. In specific applications of the invention thespacers include bone grafts in synergistic combination with osteogeniccompositions.

BACKGROUND OF THE INVENTION

Spinal fusion is indicated to provide stabilization of the spinal columnfor painful spinal motion and disorders such as structural deformity,traumatic instability, degenerative instability, and post-resectioniatrogenic instability. Fusion, or arthrodesis, is achieved by theformation of an osseous bridge between adjacent motion segments. Thiscan be accomplished within the disc space, anteriorly between contiguousvertebral bodies or posteriorly between consecutive transverseprocesses, laminae or other posterior aspects of the vertebrae.

An osseous bridge, or fusion mass, is biologically produced by the bodyupon skeletal injury. This normal bone healing response is used bysurgeons to induce fusion across abnormal spinal segments by recreatingspinal injury conditions along the fusion site and then allowing thebone to heal. A successful fusion requires the presence of osteogenic orosteopotential cells, adequate blood supply, sufficient inflammatoryresponse, and appropriate preparation of local bone. This biologicalenvironment is typically provided in a surgical setting bydecortication, or removal of the outer, cortical bone to expose thevascular, cancellous bone, and the deposition of an adequate quantity ofhigh quality graft material.

A fusion or arthrodesis procedure is often performed to treat an anomolyinvolving an intervertebral disc. Intervertebral discs, located betweenthe endplates of adjacent vertebrae, stabilize the spine, distributeforces between vertebrae and cushion vertebral bodies. A normalintervertebral disc including a semi-gelatinous component, the nucleuspulposus, which is surrounded and confined by an outer, fibrous ringcalled the annulus fibrosis. In a healthy, undamaged spine, the annulusfibrosis prevents the nucleus pulposus from protruding outside the discspace.

Spinal discs may be displaced or damaged due to trauma, disease oraging. Disruption of the annulus fibrosis allows the nucleus pulposus toprotrude into the vertebral canal, a condition commonly referred to as aherniated or ruptured disc. The extruded nucleus pulposus may press onthe spinal nerve, which may result in nerve damage, pain, numbness,muscle weakness and paralysis. Intervertebral discs may also deterioratedue to the normal aging process or disease. As a disc dehydrates andhardens, the disc space height will be reduced leading to instability ofthe spine, decreased mobility and pain.

Sometimes the only relief from the symptoms of these conditions is adiscectomy, or surgical removal of a portion or all of an intervertebraldisc followed by fusion of the adjacent vertebrae. The removal of thedamaged or unhealthy disc will allow the disc space to collapse.Collapse of the disc space can cause instability of the spine, abnormaljoint mechanics, premature development of arthritis or nerve damage, inaddition to severe pain. Pain relief via discectomy and arthrodesisrequires preservation of the disc space and eventual fusion of theaffected motion segments.

Bone grafts are often used to fill the intervertebral space to preventdisc space collapse and promote fusion of the adjacent vertebrae acrossthe disc space. In early techniques, bone material was simply disposedbetween the adjacent vertebrae, typically at the posterior aspect of thevertebrae, and the spinal column was stabilized by way of a plate or rodspanning the affected vertebrae. Once fusion occurred the hardware usedto maintain the stability of the segment became superfluous and was apermanent foreign body. Moreover, the surgical procedures necessary toimplant a rod or plate to stabilize the level during fusion werefrequently lengthy and involved.

It was therefore determined that a more optimal solution to thestabilization of an excised disc space is to fuse the vertebrae betweentheir respective end plates, preferably without the need for anterior orposterior plating. There have been an extensive number of attempts todevelop an acceptable intra-discal implant that could be used to replacea damaged disc and maintain the stability of the disc interspace betweenthe adjacent vertebrae, at least until complete arthrodesis is achieved.To be successful the implant must provide temporary support and allowbone ingrowth. Success of the discectomy and fusion procedure requiresthe development of a contiguous growth of bone to create a solid massbecause the implant may not withstand the cyclic compressive spinalloads for the life of the patient.

Many attempts to restore the intervertebral disc space after removal ofthe disc have relied on metal devices U.S. Pat. No. 4,878,915 toBrantigan teaches a solid metal plug. U.S. Pat. Nos. 5,044,104;5,026,373 and 4,961,740 to Ray; U.S. Pat. No. 5,015,247 to Michelson andU.S. Pat. No. 4,820,305 to Harms et al., U.S. Pat. No. 5,147,402 toBohler et al. and U.S. Pat. No. 5,192,327 to Brantigan teach hollowmetal cage structures. Unfortunately, due to the stiffness of thematerial, some metal implants may stress shield the bone graft,increasing the time required for fusion or causing the bone graft toresorb inside the cage. Subsidence, or sinking of the device into bone,may also occur when metal implants are implanted between vertebrae iffusion is delayed. Metal devices are also foreign bodies which can neverbe fully incorporated into the fusion mass.

Various bone grafts and bone graft substitutes have also been used topromote osteogenesis and to avoid the disadvantages of metal implants.Autograft is often preferred because it is osteoinductive. Bothallograft and autograft are biological materials which are replaced overtime with the patient's own bone, via the process of creepingsubstitution. Over time a bone graft virtually disappears unlike a metalimplant which persists long after its useful life. Stress shielding isavoided because bone grafts have a similar modulus of elasticity as thesurrounding bone. Commonly used implant materials have stiffness valuesfar in excess of both cortical and cancellous bone. Titanium alloy has astiffness value of 114 Gpa and 316 L stainless steel has a stiffness of193 Gpa. Cortical bone, on the other hand, has a stiffness value ofabout 17 Gpa. Moreover, bone as an implant also allows excellentpostoperative imaging because it does not cause scattering like metallicimplants on CT or MRI imaging.

Various implants have been constructed from bone or graft substitutematerials to fill the intervertebral space after the removal of thedisc. For example, the Cloward dowel is a circular graft made bydrilling an allogenic or autogenic plug from the illium. Cloward dowelsare bicortical, having porous cancellous bone between two corticalsurfaces. Such dowels have relatively poor biomechanical properties, inparticular a low compressive strength. Therefore, the Cloward dowel isnot suitable as an intervertebral spacer without internal fixation dueto the risk of collapsing prior to fusion under the intense cyclic loadsof the spine.

Bone dowels having greater biomechanical properties have been producedand marketed by the University of Florida Tissue Bank, Inc., 1 ProgressBoulevard, P.O. Box 31, S. Wing, Alachua, Fla. 32615. Unicortical dowelsfrom allogenic femoral or tibial condyles are available. The Universityof Florida has also developed a diaphysial cortical dowel havingsuperior mechanical properties. This dowel also provides the furtheradvantage of having a naturally preformed cavity formed by the existingmeduallary canal of the donor long bone. The cavity can be packed withosteogenic materials such as bone or bioceramic.

Unfortunately, the use of bone grafts presents several disadvantages.Autograft is available in only limited quantities. The additionalsurgery also increases the risk of infection and blood loss and mayreduce structural integrity at the donor site. Furthermore, somepatients complain that the graft harvesting surgery causes moreshort-term and long-term pain than the fusion surgery.

Allograft material, which is obtained from donors of the same species,is more readily obtained. However, allogenic bone does not have theosteoinductive potential of autogenous bone and therefore may provideonly temporary support. The slow rate of fusion using allografted bonecan lead to collapse of the disc space before fusion is accomplished.

Both allograft and autograft present additional difficulties. Graftalone may not provide the stability required to withstand spinal loads.Internal fixation can address this problem but presents its owndisadvantages such as the need for more complex surgery as well as thedisadvantages of metal fixation devices. Also, the surgeon is oftenrequired to repeatedly trim the graft material to obtain the correctsize to fill and stabilize the disc space. This trial and error approachincreases the length of time required for surgery. Furthermore, thegraft material usually has a smooth surface which does not provide agood friction fit between the adjacent vertebrae. Slippage of the graftmay cause neural and vascular injury, as well as collapse of the discspace. Even where slippage does not occur, micromotion at thegraft/fusion-site interface may disrupt the healing process that isrequired for fusion.

Several attempts have been made to develop a bone graft substitute whichavoids the disadvantages of metal implants and bone grafts whilecapturing advantages of both. For example Unilab, Inc. markets variousspinal implants composed of hydroxyapatite and bovine collagen. In eachcase developing an implant having the biomechanical properties of metaland the biological properties of bone without the disadvantages ofeither has been extremely difficult or impossible.

A need has remained for fusion spacers which stimulate bone ingrowth andavoid the disadvantages of metal implants yet provide sufficientstrength to support the vertebral column until the adjacent vertebraeare fused.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, spinal spacers andcompositions are provided for fusion of a motion segment. The spacersinclude a load bearing member sized for engagement within a spacebetween adjacent vertebrae to maintain the space and an effective amountof an osteogenic composition to stimulate osteoinduction. The osteogeniccomposition includes a substantially pure osteogenic factor in apharmaceutically acceptable carrier. In one embodiment the load bearingmember includes a bone graft impregnated with an osteogenic composition.In another embodiment, the osteogenic composition is packed within achamber defined in the graft. The grafts include bone dowels, D-shapedspacers and cortical rings.

One object of the invention is to provide spacers for engagement betweenvertebrae which encourages bone ingrowth and avoids stress shielding.Another object of the invention is to provide a spacer which restoresthe intervertebral disc space and supports the vertebral column whilepromoting bone ingrowth.

One benefit of the spacers of the present invention is that they combinethe advantages of bone grafts with the advantages of metals, without thecorresponding disadvantages. An additional benefit is that the inventionprovides a stable scaffold for bone ingrowth before fusion occurs. Stillanother benefit of this invention is that it allows the use of bonegrafts without the need for metal cages or internal fixation, due to theincreased speed of fusion. Other objects and further benefits of thepresent invention will become apparent to persons of ordinary skill inthe art from the following written description and accompanying FIGURES.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of a bone dowel according to thisinvention.

FIG. 2 shows bilateral dowel placement between L5 and the sacrum.

FIG. 3 is a perspective view of a cortical dowel having a chamber.

FIG. 4 is a side perspective view of a dowel according to thisinvention.

FIG. 5 is a cross-section of another dowel of this invention.

FIG. 6 is a side elevational view of the dowel shown in FIG. 5.

FIG. 7 is a side elevational view of another dowel provided by thisinvention.

FIG. 8 is a detail of the threads of the dowel shown in FIG. 7.

FIG. 9 is an insertion device for inserting the spacers of thisinvention.

FIG. 10A is a side perspective view of the dilation of a disc space.

FIG. 10B is a side elevational view of the dilation of a disc space.

FIG. 11A shows the seating of a single barrel outer sleeve.

FIG. 11B is a side elevational view showing the outer sleeve in place.

FIG. 12 shows the seating of a double barrel outer sleeve.

FIG. 13 shows the seating of the outer sleeve.

FIG. 14 shows the reaming of the disc space.

FIG. 15 depicts the reamer used in FIG. 14.

FIG. 16 shows the tapping of the disc space.

FIG. 17 shows the tap used in FIG. 16.

FIG. 18 shows an inserter engaged to a dowel.

FIG. 19 shows the inserter of FIG. 18 within a sleeve.

FIG. 20 depicts insertion of a dowel.

FIG. 21 is a side perspective view of a dural retractor.

FIG. 22 is a side elevational view of a guide protector.

FIG. 23 shows the insertion of the guide protector shown in FIG. 22.

FIG. 24 is a partial cross-section of a spine showing bilateralplacement of two dowels.

FIG. 25 is a partial cross-section of a spine with a cortical ringimplanted.

FIG. 26 is a cortical ring packed with an osteogenic material.

FIG. 27 is yet another cortical ring embodiment provided by thisinvention.

FIG. 28 is another embodiment of a cortical ring provided by thisinvention.

FIG. 29 is a D-shaped spacer of this invention.

FIG. 30 is a front perspective view of the spacer of FIG. 29.

FIG. 31 is a front elevational view of the spacer depicted in FIG. 29.

FIG. 32 is a top perspective view of the spacer of FIG. 29 showing thechamber packed with a collagen sponge.

FIG. 33 is a top elevational view of a collagen sponge.

FIG. 34 is an implant insertion device.

FIG. 35 is a D-spaced spacer of this invention having a tool engaginghole.

FIG. 36 is a front elevational view of the spacer FIG. 35.

FIG. 37 depicts a side elevational view of an implanting tool.

FIG. 38 is top elevational view of another embodiment of the spacer.

FIG. 39 is a top elevational view of another embodiment of the spacer.

FIG. 40 is a top perspective view of another embodiment of the spacersof this invention having teeth.

FIG. 41 is a top elevational view of another embodiment of the spacerhaving blades.

FIG. 42 is a front elevational view of the spacer of FIG. 41.

FIG. 43 is a side elevational view of an autograft crock dowel.

FIG. 44 is a side elevational view of an autograft tricortical dowel.

FIG. 45 is a side elevational view of an autograft button dowel.

FIG. 46 is a side elevational view of a hybrid autograftbutton/allograft crock dowel.

FIG. 47 is a perspective view of a threaded cortical threaded diaphysialdowel having an osteogenic composition packed in the chamber.

FIG. 48 is a side perspective view of a dowel with an osteogeniccomposition packed within the chamber.

FIG. 49 is a side perspective view of a dowel with a ceramic carrierpacked within the chamber.

FIG. 50 is a side perspective view of an axial test fixture for testingdowels of this invention.

FIG. 51 is a front cross-sectional view of the fixture of FIG. 50.

FIG. 52 is a side cross-sectional view of the fixture of FIGS. 50 and51.

FIG. 53 compares the compressive strength of a threaded cortical dowelto in vivo spinal loads.

FIG. 54 compares the compressive strength of the load bearing members ofthis invention to other known graft materials.

FIG. 55 compares the compressive strength of the a load bearing memberof this invention to fusion cages.

FIG. 56 compares the fatigue loading values for various spinal implantsin axial compression.

FIG. 57 is a side elevational view of a multi-axial loading testfixture.

FIG. 58 is a front elevational view of the fixture shown in FIG. 57.

FIG. 59 compares insertion torque values for threaded cortical dowelsand other threaded fusion spacers.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated spacers, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

The present invention provides bone grafts in synergistic combinationwith an osteogenic material, such as a bone morphogenic protein (BMP).The combination of BMP with a bone graft provides the advantages of abone graft while enhancing bone growth into and incorporation of thegraft, resulting in fusion quicker than with graft alone. The quickerfusion rates provided by this invention compensate for the lessdesirable biomechanical properties of graft and makes the use ofinternal fixation and metal interbody fusion devices unnecessary. Thespacers of this invention are not required to support the cyclic loadsof the spine for very long because of the quick fusion rates whichreduce the biomechanical demands on the spacer. Therefore this inventioncapitalizes on the advantages of graft while avoiding the disadvantages.

The spinal spacers of this invention include a load bearing member sizedfor engagement within a space between adjacent vertebrae to maintain thespace. The load bearing member is a bone graft in synergisticcombination with an osteogenic material. The bone graft is any suitablebone material, preferably of human origin, including tibial, fibial,humeral, iliac, etc. The load bearing members of this invention includeflat D-shaped spacers, bone dowels, cortical rings and any suitablyshaped load bearing member composed of bone. A preferred load bearingmember is obtained from the diaphysis of a long bone having a medullarycanal which forms a natural chamber in the graft.

This invention provides the further advantage of exploiting thediscovery that bone is an excellent carrier for osteogenic factors suchas bone morphogenic proteins. Hydroxyapatite which is very similar inchemical composition to the mineral in cortical bone is an osteogenicfactor-binding agent which controls the rate of delivery of certainproteins to the fusion site. Calcium phosphate compositions such ashydroxyapatite are thought to bind bone morphogenic proteins and preventBMP from prematurely dissipating from the spacer before fusion canoccur. It is further believed that retention of the BMP by the agentpermits the protein to initiate the transformation of mesenchymal stemcells into bone producing cells (osteoblasts) within the device at arate that is conducive to complete and rapid bone formation andultimately fusion across the disc space. The spacers of this inventionhave the advantage of including a load bearing member composed of bonewhich naturally binds and provides controlled delivery of osteogenicfactors such as bone morphogenic proteins.

This invention also capitalizes on the discovery that cortical bone,like metal, can be conveniently machined into the various shapesdisclosed herein. In some embodiments, the load bearing members definethreads on an outer surface. Machined surfaces, such as threads, provideseveral advantages that were previously only available with metalimplants. Threads allow better control of spacer insertion than can beobtained with a smooth surface. This allows the surgeon to moreaccurately position the spacer which is extremely important around thecritical neurological and vascular structures of the spinal column.Threads and the like also provide increased surface area whichfacilitates the process of bone healing and creeping substitution forreplacement of the donor bone material and fusion. These features alsoincrease post-operative stability of the spacer by engaging the adjacentvertebral endplates and anchoring the spacer to prevent expulsion. Thisis a major advantage over smooth grafts. Surface features also stabilizethe bone-spacer interface and reduce micromotion to facilitateincorporation and fusion.

In one specific embodiment depicted in FIG. 1, the load bearing memberof the spacer 10 is a bone dowel 11 soaked with an effective amount ofan osteogenic composition to stimulate osteoinduction. Preferably, theosteogenic composition includes a substantially pure osteogenic factorin a pharmaceutically acceptable carrier. The dowel 10 includes a wall12 sized for engagement within the intervertebral space IVS to maintainthe space IVS. The wall 12 defines an outer engaging surface 13 forcontacting the adjacent vertebrae. The wall 12 is preferablycylindrically so that the bone dowel 10 has a diameter d which is largerthan the height h of the space IVS between adjacent vertebrae V or theheight of the space between the lowest lumbar vertebrae L5 and thesacrum S as depicted in FIG. 2.

In another embodiment 20 depicted in FIG. 3, the load bearing member isa bone dowel 21 which includes a wall 22 having an engagement surface23. The wall 22 defines a chamber 25 therethrough. Preferably, the loadbearing member is a bone graft obtained from the diaphysis of a longbone having a medullary canal which forms the chamber 25. The chamber 25is most preferably packed with an osteogenic composition to stimulateosteoinduction. The chamber 25 is preferably defined through a pair ofouter engaging surfaces 23 so that the composition has maximum contactwith the endplates of the adjacent vertebrae. Referring now to FIG. 4,the spacer 21 includes a solid protective wall 26 which is positionableto protect the spinal cord from escape or leakage of the osteogeniccomposition 30 within the chamber 25. In anterior approaches, theprotective wall 26 is posterior. Preferably, the osteogenic composition30 has a length which is greater than the length of the chamber (FIGS. 5and 6) and the composition 30 is disposed within the chamber 25 tocontact the end plates of adjacent vertebrae when the spacer 20′ isimplanted between the vertebrae. This provides better contact of thecomposition with the end plates to stimulate osteoinduction.

Various features can be machined on the outer surfaces of the dowels ofthis invention. In one embodiment shown in FIG. 7, the dowel 40 includesan outer engaging surface 41 defining threads 42. The initial or starterthread 47 is adjacent the protective wall 26′. As shown more clearly inFIG. 8, the threads are preferably uniformally machined threads whichinclude teeth 43 having a crest 44 between a leading flank 45 and anopposite trailing flank 46. Preferably the crest 44 of each tooth 43 isflat. In one specific embodiment, the crest 44 of each tooth 43 has awidth w of between about 0.020 inches and about 0.030 inches. Thethreads 42 preferably define an angle α between the leading flank 45 andthe trailing flank 46 of adjacent ones of said teeth 43. The angle α ispreferably between about 50 degrees and 70 degrees. Each tooth 43preferably has a height h′ which is about 0.030 inches and about 0.045inches.

Referring again to FIG. 7, in some embodiments, the dowel 40 is providedwith a tool engaging hole 49 in a wall 48 opposite the solid protectivewall 26′. The tool engaging hole 49 is provided in a surface of thedowel which is adjacent the surgeon and opposite the initial thread 47.For an anterior procedure, the tool engaging tool hole 49 would beprovided in the anterior surface 48 of the dowel 40. Other machinedfeatures are contemplated in the outer or bone engaging surfaces 41.Such machine features include surface roughenings such as knurlings andratchetings.

In a most preferred embodiment, the tool engaging hole 49 is threaded toreceive a threaded tip of an implanting tool. The inserter 60 shown inFIG. 9 includes a handle portion 61 and a shaft 62 extends from thehandle 61. The distal end 63 of the shaft 62 includes a tip 65 whichmates with the tool engaging hole 49. Preferably the tip 65 and the toolengaging hole 49 have corresponding mating threads 66, 49A. The inserter60 preferably includes a T-handle for spacer control and positioning.The shaft 62 of the inserter 60 also includes a depth stop 64.Preferably the inserter 60 includes means for rotating the threaded tip65. Knob 68 is engaged to the tip 65 through an intershaft extendingthrough an internal bore (not shown) in the handle 61 and in the shaft62. The tip 65 is preferably at the end of the intershaft with theintershaft rotatingly mounted within the handle 61 and the shaft 62.

The spacers of this invention can be inserted using conventionaltechniques. In accordance with additional aspects of the presentinvention, methods for implanting an interbody fusion spacer, such asthe spacer 40, are contemplated. These methods are also disclosed incommonly assigned, co-pending U.S. patent application Ser. No.08/604,874, METHODS AND INSTRUMENTS FOR INTERBODY FUSION. As apreliminary step, it is necessary to locate appropriate starting pointsfor implanting the fusion spacer, preferably bilaterally. In the firststep of an anterior approach, a distractor 75 is disposed between thevertebral end plates E to dilate the L4-L5 or L5-S1 disc space (FIGS.10A and 10B). (It is understood, of course, that this procedure can beapplied at other vertebral levels). In the second step, shown in FIG.11A, an outer sleeve 76 is disposed about the disc space IVS. The outersleeve 76 can be configured to positively engage the anterior aspect ofthe vertebral bodies to firmly, but temporarily, anchor the outer sleeve76 in position. In essence, this outer sleeve 76 operates as a workingchannel for this approach. In a preferred embodiment, a single barrelouter sleeve 76 a is first inserted (FIG. 11B) followed by a doublebarrel outer sleeve 76 b, (FIG. 12), finally followed by the outersleeve 76 (FIG. 13). One purpose of this tripartite sleeve system is toprovide an enlarged working channel for preparing the vertebrae andimplanting the fusion spacer. In the step shown in FIG. 14, a drill orreamer 77 (FIG. 15) is extended through the outer sleeve 76 and used todrill out circular openings in the adjacent vertebral bodies. Theopenings can be tapped (FIG. 16) with a tap 78 (FIG. 17) to facilitatescrew insertion of the fusion spacer 10, although this step is notnecessary.

The fusion spacer 40 is then engaged by an implant driver 60, 60′ (FIGS.18 & 19) and extended through the outer sleeve 76 as shown in FIG. 13.The spacer is then inserted into the disc space IVS until the initialthread 47 contacts the bone opening as shown in FIG. 20. The implantdriver 60 can then be used to screw thread the fusion spacer into thetapped or untapped opening formed in the vertebral and end plate E. Oncethe dowel 40 is properly positioned, the knob 68 of the tool 60 can beturned to rotate the threaded tip 65 and disengage the tip 65 from thehole 49 of the dowel 40. The inserter 60 and the sleeve 76 can bewithdrawn from the surgical site leaving the dowel 40 in place. It isunderstood that in this step, other suitable driving tools could beused. It can been seen that once implanted the closed posterior end 26is directed toward the posterior aspect of the vertebrae. The chamber 25packed with an osteogenic material is positioned so that the osteogenicmaterial contacts the end plates.

The spacers of this invention may also be used with posteriorapproaches. The steps of the posterior approach are similar to those ofthe prior anterior approach except that the tools are introducedposteriorly at the instrumented motion segment. This approach mayrequire decortication and removal of vertebral bone to accept the outersleeve 76. A dural retractor 80 as shown in FIG. 21 may be used toretract and protect the spinal cord and accessory tissues. The retractor80 includes a handle 81 which preferably includes a bend 82 tofacilitate manipulation of the tool. The dural retractor 80 has an end83 which is attached to the handle portion 81. The end 83 preferablyincludes a curve 84 which is configured to safely cradle the spinalcord.

With the spinal cord safely retracted, a seat guide protector 85 (FIG.22) can be pounded into position as shown in FIG. 23. The seat guideprotector 85 can be similar to the sleeve 76 described above. Varioustools, such as extractors, reamers and taps can be inserted through theseat guide protector similar as described above. The fusion spacer 40can be inserted through the protector 85 into the dilated disc space.

With either the anterior or posterior approaches, the position of thefusion spacer 40 with respect to the adjacent vertebrae can be verifiedby radiograph or other suitable techniques for establishing the angularrelationship between the vertebrae. Alternatively, the preferred depthof insertion of the spacer can be determined in advance and measuredfrom outside the patient as the spacer is positioned between thevertebrae. The depth of insertion of the fusion spacer can beascertained using depth markings (not shown) on the implant driver 60.

The spacers of this invention can also be inserted using laproscopictechnology as described in Sofamor Danek USA's Laproscopic Bone DowelSurgical Technique,© 1995, 1800 Pyramid Place, Memphis, Tenn. 38132,1-800-933-2635. Devices of this invention can be convenientlyincorporated into Sofamor Danek's laproscopic bone dowel system thatfacilitates anterior interbody fusions with an approach that is muchless surgical morbid than the standard open anterior retroperitonealapproaches. This system includes templates, trephines, dilators,reamers, ports and other devices required for laproscopic dowelinsertion.

Bilateral placement of dowels 40 is preferred as shown in FIGS. 2 and24. This configuration provides a substantial quantity of bone graftavailable for the fusion. The dual bilateral cortical dowels 40 resultin a significant area of cortical bone for load bearing and long-termincorporation via creeping substitution, while giving substantial areafor placement of osteogenic autogenous bone and boney bridging acrossthe disc space. Comparing FIG. 24 to FIG. 25, it can be seen thatbilateral placement of dowels 40 provides a greater surface area of bonematerial than a single ring allograft 50 which provides only a singlechamber 55 for packing with osteogenic material 30. The dual dowelplacement results in two chambers 25 that can be filled with anosteogenic composition. Additionally, osteogenic material 30 such ascancellous bone or BMP in a biodegradable carrier may be packed aroundthe dowels. This provides for the placement of a significant amount ofosteogenic material as well as four columns 35, 36, 37, 38 of corticalbone for load bearing.

The load bearing member may also include other grafts such as corticalrings as shown in FIG. 26. Such cortical rings 50 are obtained by across-sectional slice of the diaphysis of a long bone and includesuperior surface 51 and inferior surface 52. The graft shown in FIG. 26includes an outer surface 53 which is adjacent and between the superior51 and inferior 52 surfaces. In one embodiment bone growth thru-holes 53a are defined through the outer surface 53 to facilitate fusion. Theholes 53 a allows mesenchymal stem cells to creep in and BMP protein todiffuse out of the graft. This facilitates bone graft incorporation andpossibly accelerates fusion by forming anterior and lateral bonebridging outside and through the device. In another embodiment the outersurface 53 defines a tool engaging hole 54 for receiving an implantingtool. In a preferred embodiment, at least one of the superior and/orinferior surfaces 51, 52 are roughened for gripping the end plates ofthe adjacent vertebrae. The surface roughenings may include teeth 56 onring 50′ as shown in FIG. 27 or waffle pattern 57 as shown on ring 50″in FIG. 28. When cortical rings are used as the graft material the ring50 may be trimmed for a more uniform geometry as shown in FIG. 26 orleft in place as shown in FIG. 28.

In another specific embodiment, spacers are provided for engagementbetween vertebrae as depicted in FIGS. 29-31. Spacers of this inventioncan be conveniently incorporated into current surgical procedures suchas, the Smith-Robinson technique for cervical fusion (Smith, M. D., G.W. and R. A. Robinson, M. D., “The Treatment of Certain Cervical-SpineDisorders By Anterior Removal Of The Intervertebral Disc And InterbodyFusion”, J. Bone And Joint Surgery, 40-A:607-624 (1958) and Cloward, M.D., R. B., “The Anterior Approach For Removal Of Ruptured CervicalDisks”, in meeting of the Harvey Cushing Society, Washington, D.C., Apr.22, 1958). In such procedures, the surgeon prepares the endplates of theadjacent vertebral bodies to accept a graft after the disc has beenremoved. The endplates are generally prepared to be parallel surfaceswith a high speed burr. The surgeon then typically sculpts the graft tofit tightly between the bone surfaces so that the graft is held bycompression between the vertebral bodies. The bone graft is intended toprovide structural support and promote bone ingrowth to achieve a solidfusion of the affected joint. The spacers of this invention avoid theneed for this graft sculpting as spacers of known size and dimensionsare provided. This invention also avoids the need for a donor surgerybecause the osteoinductive properties of autograft are not required. Thespacers can be combined with osteoinductive materials that makeallograft osteoinductive. Therefore, the spacers of this invention speedthe patient's recovery by reducing surgical time, avoiding a painfuldonor surgery and inducing quicker fusion.

The spacer 110 includes an anterior wall 111 having opposite ends 112,113, a posterior wall 115 having opposite ends 116, 117 and two lateralwalls 120, 121. Each of the lateral walls 120, 121 is connected betweenthe opposite ends 112, 113, 116, 117 of the anterior 111 and posterior115 walls to define a chamber 130. The walls are each composed of boneand also include the superior face 135 which defines a first opening 136in communication with the chamber 130. The superior face 135 includes afirst friction or vertebral engaging surface 137. As shown in FIG. 31,the walls further include an opposite inferior face 138 defining asecond opening 139 which is in communication with the chamber 130. Thechamber 130 is preferably sized to receive an osteogenic composition tofacilitate bone growth. The inferior face 138 includes a second frictionor second vertebral engaging surface (not shown) which is similar to oridentical to the first friction or vertebral engaging surface 137.

In one specific embodiment for an intervertebral disc replacementspacer, a hollow D-shaped spinal spacer is provided. The anterior wall111 as shown in FIGS. 29-31 is convexly curved. This anterior curvatureis preferred to conform to the geometry of the adjacent vertebral boneand specifically to the harder cortical bone of the vertebrae. TheD-shape of the spacer 110 also prevents projection of the anterior wall111 outside the anterior aspect of the disc space, which can beparticularly important for spacers implanted in the cervical spine.

In one specific embodiment shown in FIGS. 32 and 33, the D-shaped spacer110 includes a collagen sponge 148 having a Width w and length l whichare each slightly greater than the width W and length L of the chamber.In a preferred embodiment, the sponge 148 is soaked with freeze driedrhBMP-2 reconstituted in buffered physiological saline and thencompressed into the chamber 130. The sponge 148 is held within thechamber 130 by the compressive forces provided by the sponge 148 againstthe walls 111, 115, 120, 121 of the spacer 110.

The spacers are shaped advantageously for cervical arthrodesis. The flatposterior and lateral walls 115, 120 and 121, as shown in FIG. 29, canbe easily incorporated into Smith Robinson surgical fusion technique.After partial or total discectomy and distraction of the vertebralspace, the surgeon prepares the end plates for the spacer 110 preferablyto create flat posterior and lateral edges. The spacer 110 fits snuglywith its flat surfaces against the posterior and lateral edges whichprevents medial and lateral motion of the spacer 110 into vertebralarteries and nerves. This also advantageously reduces the time requiredfor the surgery by eliminating the trial and error approach to achievinga good fit with bone grafts because the spacers can be provided inpredetermined sizes.

Devices such as the spacer 110 or dowel 40, which are not provided withan insertion tool hole, can be inserted into the fusion site during anopen or percutaneous surgery using an insertion device such as the onedepicted in FIG. 34. The inserter 150 includes a handle 151 withknurlings or other suitable patterns to enhance manual gripping of thehandle. A shaft 152 extends from the handle 151 and is generally dividedinto two portions: a solid portion 153 and a split jaw portion 154. Thesplit jaw portion 154 is at the distal end of the shaft 152 opposite thehandle 151. In the preferred embodiment, the split jaw portion 154includes two jaws 156 each having an offset gripping surface 158 attheir free ends. As depicted in FIG. 34 the split jaw portions 154 aremovable from a fully opened position as represented by the fullyseparated position of the gripping surfaces 158. The split jaw portion154 is closeable to a fully closed position in which the two jaws 156are in contact with one another. In the fully closed position, thegripping surfaces, identified as 158′ in FIG. 34, are separated by adistance sufficiently close to grip a hollow spacer 110 therebetween. Inparticular, the closed gripping surfaces 158′ contact the side surfacesof the two lateral walls 120, 121 of the spacer 110. In one preferredembodiment, the gripping surfaces 158 are roughened or knurled toenhance the grip on the spacer 110.

The inserter 150 further includes a sleeve 160 that is concentricallydisposed around shaft 152. Preferably the sleeve 160 defines an innerbore 161 with a first portion 162 having a diameter slightly greaterthan the diameter of shaft 152. The internal bore 161 includes a flaredportion 163 at its distal end 164. In the preferred embodiment, when thejaws 156 of the split jaw portion 154 are in their fully openedposition, the jaws contact the flared portion 63 of the bore 161.

In the use of the inserter 150, the sleeve 160 is slid along the shaft152, and more particularly along the opened jaws 156, to push the jawstogether. As the jaws are pushed together, the gripping surfaces 158engage and firmly grip a spacer 110 as described above. This insertercan then be extended percutaneously into the surgical site to implant aspacer 110 in the intra-discal space. Once the spacer is properlypositioned, the sleeve 160 can be moved back toward the handle 151, sothat the natural resilience of the two jaws 156 cause them to spreadapart, thereby releasing the spacer 110. The inserter 150 can then bewithdrawn from the surgical site with the jaws fully opened, or thesleeve can be advanced along the shaft once the gripping surfaces 158have cleared the spacer 110. Other details of a similar device aredisclosed in commonly assigned, pending U.S. application Ser. No.08/697,784, IMPLANT INSERTION DEVICE. Metal spacers, insertion devicesand methods relating to the same are disclosed in commonly assigned andco-pending applications: U.S. patent application Ser. No. 08/603,675,VERTEBRAL SPACER and U.S. patent application Ser. No. 08/603,676,INTERVERTEBRAL SPACER.

Alternatively, the spacers of this invention may be provided with a toolengaging hole for insertion such as the tool depicted in FIG. 9.According to another specific embodiment depicted in FIGS. 35 and 36,the spacer 170 includes an anterior wall 171 defining a tool engaginghole 174. In a most preferred embodiment, the tool engaging hole 174 isthreaded for receiving a threaded implanting tool such as depicted inFIG. 37. The inserter 220 includes a handle portion 221 with knurlingsor other suitable patterns to enhance manual gripping of the handle. Ashaft 222 extends from the handle 221. The distal end 223 of the shaft222 includes a tip 225 which mates with the tool engaging hole 174.Preferably the tip 225 and tool engaging hole 174 have correspondingmating threads 226, 178. Where the tool engaging hole 174 is defined ina curved wall as shown in FIG. 35, the distal end 223 of the shaft 222preferably includes a curved portion 224 that conforms to the curvedanterior surface of the spacer. The inserter 220 also preferablyincludes a T-handle 228 for spacer control and positioning. Preferablythe inserter 120 includes means for rotating the threaded tip 225. InFIG. 37, the knob 230 is engaged to the tip 225 via an inner shaftextending through an internal bore (not shown) in the handle 221 andshaft 222. The tip 225 is preferably at the end of the inner shaft withthe inner shaft rotatingly mounted within the handle 221 and shaft 222.

In the use of the inserter 220, a spacer 170 is engaged to the threadedtip 225 with the curved portion 224 flush with the anterior wall 171.The inserter and spacer can then be extended percutaneously into thesurgical site to implant the spacer in the intra-discal space. Once thespacer 170 is properly positioned, the knob 230 can be turned to rotatethe threaded tip 225 and disengage the tip from the hole 174 of thespacer 110. The inserter 220 can then be withdrawn from the surgicalsite leaving the spacer 170 in place.

In preferred embodiments, the engaging surfaces of the spacers aremachined to facilitate engagement with the endplates of the vertebraeand prevent slippage of the spacer as is sometimes seen with smoothgraft prepared at the time of surgery. The spacer 180 may be providedwith a roughened surface 181 on one of the engaging surfaces 187 of oneor both of the superior face 185 or inferior face (not shown) as shownin FIG. 38. The roughened surface 191 of the spacer 190 may include awaffle or other suitable pattern as depicted in FIG. 39. In onepreferred embodiment shown in FIG. 40, the engaging surfaces 201 includeteeth 205 which provide biting engagement with the endplates of thevertebrae. In another embodiment (FIGS. 41 and 42), the spacer 210includes engaging surfaces 211 machined to include one or more blades212. Each blade includes a cutting edge 213 configured to pierce avertebral end-plate. The blade 212 can be driven into the bone surfaceto increase the initial stability of the spacer.

Any suitable load bearing member which can be synergistically combinedwith an osteogenic composition is contemplated. Other potential loadbearing members include allograft crock dowels (FIG. 43), tricorticaldowels (FIG. 44), button dowels (FIG. 45) and hybrid allograftbutton-allograft crock dowels (FIG. 46).

An osteogenic material can be applied to the spacers of this inventionby packing the chamber 25,130 with an osteogenic material 30,148 asshown in FIGS. 32 and 47, by impregnating the graft with a solutionincluding an osteogenic composition or by both methods combined. Thecomposition may be applied by the surgeon during surgery or the spacermay be supplied with the composition preapplied. In such cases, theosteogenic composition may be stabilized for transport and storage suchas by freeze-drying. The stabilized composition can be rehydrated and/orreactivated with a sterile fluid such as saline or water or with bodyfluids applied before or after implantation. Any suitable osteogenicmaterial or composition is contemplated, including autograft, allograft,xenograft, demineralized bone, synthetic and natural bone graftsubstitutes, such as bioceramics and polymers, and osteoinductivefactors. The term osteogenic composition used here means virtually anymaterial that promotes bone growth or healing including natural,synthetic and recombinant proteins, hormones and the like.

Autograft can be harvested from locations such as the iliac crest usingdrills, gouges, curettes and trephines and other tools and methods whichare well known to surgeons in this field. Preferably, autograft isharvested from the iliac crest with a minimally invasive donor surgery.The graft may include osteocytes or other bone reamed away by thesurgeon while preparing the end plates for the spacer.

Advantageously, where autograft is chosen as the osteogenic material,only a very small amount of bone material is needed to pack the chamber130. The autograft itself is not required to provide structural supportas this is provided by the spacer 110. The donor surgery for such asmall amount of bone is less invasive and better tolerated by thepatient. There is usually little need for muscle dissection in obtainingsuch small amounts of bone. The present invention therefore eliminatesmany of the disadvantages of autograft.

The osteogenic compositions used in this invention preferably comprise atherapeutically effective amount of a substantially pure bone inductivefactor such as a bone morphogenetic protein in a pharmaceuticallyacceptable carrier. The preferred osteoinductive factors are therecombinant human bone morphogenic proteins (rhBMPs) because they areavailable in unlimited supply and do not transmit infectious diseases.Most preferably, the bone morphogenetic protein is a rhBMP-2, rhBMP-4 orheterodimers thereof. The concentration of rhBMP-2 is generally betweenabout 0.4 mg/ml to about 1.5 mg/ml, preferably near 1.5 mg/ml. However,any bone morphogenetic protein is contemplated including bonemorphogenetic proteins designated as BMP-1 through BMP-13. BMPs areavailable from Genetics Institute, Inc., Cambridge, Mass. and may alsobe prepared by one skilled in the art as described in U.S. Pat. No.5,187,076 to Wozney et al.; U.S. Pat. No. 5,366,875 to Wozney et al.;U.S. Pat No. 4,877,864 to Wang et al.; U.S. Pat No. 5,108,922 to Wang etal.; U.S. Pat No. 5,116,738 to Wang et al.; U.S. Pat No. 5,013,649 toWang et al.; U.S. Pat. No. 5,106,748 to Wozney et al.; and PCT PatentNos. WO93/00432 to Wozney et al.; WO94/26893 to Celeste et al.; andWO94/26892 to Celeste et al. All osteoinductive factors are contemplatedwhether obtained as above or isolated from bone. Methods for isolatingbone morphogenic protein from bone are described in U.S. Pat No.4,294,753 to Urist and Urist et al., 81 PNAS 371, 1984.

The choice of carrier material for the osteogenic composition is basedon biocompatibility, biodegradability, mechanical properties andinterface properties as well as the structure of the load bearingmember. The particular application of the compositions of the inventionwill define the appropriate formulation. Potential carriers includecalcium sulphates, polylactic acids, polyanhydrides, collagen, calciumphosphates, polymeric acrylic esters and demineralized bone. The carriermay be any suitable carrier capable of delivering the proteins. Mostpreferably, the carrier is capable of being eventually resorbed into thebody. One preferred carrier is an absorbable collagen sponge marketed byIntegra LifeSciences Corporation under the trade name Helistat®Absorbable Collagen Hemostatic Agent. Another preferred carrier is anopen cell polylactic acid polymer (OPLA). Other potential matrices forthe compositions may be biodegradable and chemically defined calciumsulfates, calcium phosphates such as tricalcium phosphate (TCP) andhydroxyapatite (HA) and including injectable bicalcium phosphates (BCP),and polyanhydrides. Other potential materials are biodegradable andbiologically derived, such as bone or dermal collagen. Further matricesare comprised of pure proteins or extracellular matrix components. Theosteoinductive material may also be an admixture of BMP and a polymericacrylic ester carrier, such as polymethylmethacrylic.

For packing the chambers of the spacers of the present invention, thecarriers are preferably provided as a sponge 58,30 which can becompressed into the chamber 55 (FIG. 25) or 25 (FIG. 47) or as strips orsheets which may be folded to conform to the chamber as shown in FIG.48. Preferably, the carrier has a width and length which are eachslightly greater than the width and length of the chamber. In the mostpreferred embodiments, the carrier is soaked with a rhBMP-2 solution andthen compressed into the chamber. As shown in FIG. 47, the sponge 30 isheld within the chamber 25 by the compressive forces provided by thesponge 30 against the wall 22 of the dowel 21. It may be preferable forthe carrier to extend out of the openings of the chamber to facilitatecontact of the osteogenic composition with the highly vascularizedtissue surrounding the fusion site. The carrier can also be provided inseveral strips sized to fit within the chamber. The strips can be placedone against another to fill the interior. As with the folded sheet, thestrips can be arranged within the spacer in several orientations.Preferably, the osteogenic material, whether provided in a sponge, asingle folded sheet or in several overlapping strips, has a lengthcorresponding to the length and width of the chamber.

The most preferred carrier is a biphasic calcium phosphate ceramic. FIG.49 shows a ceramic carrier 32 packed within a dowel 40.Hydroxyapatite/tricalcium phosphate ceramics are preferred because oftheir desirable bioactive properties and degradation rates in vivo. Thepreferred ratio of hydroxyapatite to tricalcium phosphate is betweenabout 0:100 and about 65:35. Any size or shape ceramic carrier whichwill fit into the chambers defined in the load bearing member arecontemplated. Ceramic blocks are commercially available from SofamorDanek Group, B. P. 4-62180 Rang-du-Fliers, France and Bioland, 132 Routed:Espagne, 31100 Toulouse, France. Of course, rectangular and othersuitable shapes are contemplated. The osteoinductive factor isintroduced into the carrier in any suitable manner. For example, thecarrier may be soaked in a solution containing the factor.

In a preferred embodiment, an osteogenic composition is provided to thepores of the load bearing member. The bone growth inducing compositioncan be introduced into the pores in any suitable manner. For example,the composition may be injected into the pores of the graft. In otherembodiments, the composition is dripped onto the graft or the graft issoaked in a solution containing an effective amount of the compositionto stimulate osteoinduction. In either case the pores are exposed to thecomposition for a period of time sufficient to allow the liquid tothoroughly soak the graft. The osteogenic factor, preferably a BMP, maybe provided in freeze-dried form and reconstituted in a pharmaceuticallyacceptable liquid or gel carrier such as sterile water, physiologicalsaline or any other suitable carrier. The carrier may be any suitablemedium capable of delivering the proteins to the spacer. Preferably themedium is supplemented with a buffer solution as is known in the art. Inone specific embodiment of the invention, rhBMP-2 is suspended oradmixed in a carrier, such as water, saline, liquid collagen orinjectable BCP. The BMP solution can be dripped into the graft or thegraft can be immersed in a suitable quantity of the liquid. In a mostpreferred embodiment, BMP is applied to the pores of the graft and thenlypholized or freeze-dried. The graft-BMP composition can then be frozenfor storage and transport.

Advantageously, the intervertebral spacers of the present invention maynot require internal fixation. The spacers are contained by thecompressive forces of the surrounding ligaments and muscles, and thedisc annulus if it has not been completely removed. Temporary externalimmobilization and support of the instrumented and adjacent vertebrallevels, with a cervical collar, lumbar brace or the like, is generallyrecommended until adequate fusion is achieved.

Although the spacers and compositions of this invention make the use ofmetal devices typically unnecessary, the invention may be advantageouslycombined with such devices. The bone graft-osteogenic compositions ofthe invention can be implanted within any of the various prior art metalcages.

The following specific examples are provided for purposes ofillustrating the invention, and no limitations on the invention areintended thereby.

EXPERIMENTAL I: PREPARATION OF DEVICES Example 1 Diaphysial CorticalBone Dowel

A consenting donor (i.e., donor card or other form of acceptance toserve as a donor) was screened for a wide variety of communicablediseases and pathogens, including human immunodeficiency virus,cytomegalovirus, hepatitis B, hepatitis C and several other pathogens.These tests may be conducted by any of a number of means conventional inthe art, including but not limited to ELISA assays, PCR assays, orhemagglutination. Such testing follows the requirements of: (i) AmericanAssociation of Tissue Banks, Technical Manual for Tissue Banking,Technical Manual—Musculoskeletal Tissues, pages M19-M20; (ii) The Foodand Drug Administration, Interim Rule, Federal Register/Vol. 50, No.238/Tuesday, Dec. 14, 1993/Rules and Regulations/65517, D. InfectiousDisease Testing and Donor Screening, (iii) MMWR/Vol. 43/No. RR-8,Guidelines for Preventing Transmission of Human Immunodeficiency VirusThrough Transplantation of Human Tissue and Organs, pages 4-7; (iv)Florida Administrative Weekly, Vol. 10, No. 34, Aug. 21, 1992,59A-1.001-014 59A-1.005(12)(c), F.A.C., (12)(a)-(h), 59A-1.005(15),F.A.C., (4)(a)-(8). In addition to a battery of standard biochemicalassays, the donor, or their next of kin, was interviewed to ascertainwhether the donor engaged in any of a number of high risk behaviors suchas having multiple sexual partners, suffering from hemophilia, engagingin intravenous drug use etc. After the donor was ascertained to beacceptable, the bones useful for obtention of the dowels were recoveredand cleaned.

A dowel was obtained as a transverse plug from the diaphysis of a longbone using a diamond tipped cutting bit which was water cleaned andcooled. The bit was commercially available (Starlite, Inc) and had agenerally circular nature and an internal vacant diameter between about10 mm to about 20 mm. The machine for obtention of endo- and corticaldowels consisted of a pneumatic driven miniature lathe which isfabricated from stainless steel and anodized aluminum. It has a springloaded carriage which travels parallel to the cutter. The carriage rideson two runners which are 1.0 inch stainless rods and has a traveldistance of approximately 8.0 inches. One runner has set pin holes onthe running rod which will stop the carriage from moving when the setpin is placed into the desired hole. The carriage is moveable from sideto side with a knob which has graduations in metric and in English. Thisallows the graft to be positioned. On this carriage is a vice whichclamps the graft and holds it in place while the dowel is being cut. Thevice has a cut out area in the jaws to allow clearance for the cutter.The lathe has a drive system which is a pneumatic motor with a valvecontroller which allows a desired RPM to be set.

First, the carriage is manually pulled back and locked in place with aset pin. Second, the graft is loaded into the vice and is aligned withthe cutter. Third, the machine is started and the RPM is set, by using aknob on the valve control. Fourth, the set pin, which allows the graftto be loaded onto the cutter to cut the dowel. Once the cutter has cutall the way through the graft the carriage will stop on a set pin.Fifth, sterile water is used to eject dowel out of the cutter. It isfully autoclavable and has a stainless steel vice and/or clampingfixture to hold grafts for cutting dowels. The graft can be positionedto within 0.001″ of an inch which creates dowel uniformity during thecutting process.

The cutter used in conjunction with the above machine can produce dowelsranging from 5 mm to 30 mm diameters and the sizes of the cutters are10.6 mm; 11.0 mm; 12.0 mm; 13.0 mm; 14.0 mm; 16.0 mm; and 18.0 mm. Thecomposition of the cutters is stainless steel with a diamond powdercutting surface which produces a very smooth surface on the wall of thedowels. In addition, sterile water is used to cool and remove debrisfrom graft and/or dowel as the dowel is being cut (hydro infusion). Thewater travels down through the center of the cutter to irrigate as wellas clean the dowel under pressure. In addition, the water aides inejecting the dowel from the cutter.

The marrow was then removed from the medullary canal of the dowel andthe cavity cleaned to create of chamber. The final machined product maybe stored, frozen or freeze-dried and vacuum sealed for later use.

Example 2 Threaded Dowels

A diaphysial cortical bone dowel is prepared as described above. Theplug is then machined, preferably in a class 10 clean room, to thedimensions desired. The machining is preferably conducted on a lathesuch as a jeweler's lathe or machining tools may be specificallydesigned and adapted., for this purpose. A hole is then drilled throughthe anterior wall of the dowel. The hole is then tapped to receive athreaded insertion tool.

Example 3 Bone Dowel Soaked with rhBMP-2

A threaded dowel is obtained through the methods of Examples 1 and 2.

A vial containing 4.0 mg of lyphilized rhBMP-2 (Genetics Institute) isconstituted with 1 mL sterile water (Abbott Laboratories) for injectionto obtain a 4.0 mg/mL solution is follows:

1. Using a 3-cc syringe and 22 G needle, slowly inject 1.0 mL sterilewater for injection into the vial containing lyphilized rhBMP-2.

2. Gently swirl the vial until a clear solution is obtained. Do notshake.

The dilution scheme below is followed to obtain the appropriate rhBMP-2concentration. This dilution provides sufficient volume for two dowels.The dilutions are performed as follows:

1. Using a 5-cc syringe, transfer 4.0 mL of MFR 906 buffer (GeneticsInstitute) into a sterile vial.

2. Using a 1-cc syringe, transfer 0.70 mL reconstituted rhBMP-2 into thevial containing the buffer.

3. Gently swirl to mix.

DILUTION SCHEME INITIAL rhBMP-2 rhBMP-2 MFR-842 FINAL rhBMP-2CONCENTRATION VOLUME VOLUME CONCENTRATION (mg/mL) (mL) (mL) (mg/mL) 4.00.7 4.0 0.60

1. Using a 3-cc syringe and 22 G needle, slowly drip 2.0 mL of 0.60mg/mL rhBMP-2 solution onto the Bone Dowel.

2. Implant immediately.

Example 4 Bone Dowel Packed with BMP-2/Collagen Composition

A threaded dowel is obtained through the methods of Examples 1 and 2.

A vial containing 4.0 mg of lyphilized rhBMP-2 (Genetics Institute) isconstituted with 1 mL sterile water (Abbott Laboratories) for injectionto obtain a 4.0 mg/mL solution as follows:

1. Using a 3-cc syringe and 22 G needle, slowly inject 1.0 mL sterilewater for injection into the vial containing lyphilized rhBMP-2.

2. Gently swirl the vial until a clear solution is obtained. Do notshake.

The dilution scheme below is followed to obtain the appropriate rhBMP-2concentration. The dilutions are performed as follows:

1. Using a 3-cc syringe, transfer 2.5 mL of MFR-842 buffer (GeneticsInstitute) into a sterile vial.

2. Using a 1-cc syringe, transfer 0.30 mL of 4.0 mg/mL reconstitutedrhBMP-2 into the vial containing the buffer.

3. Gently swirl to mix.

DILUTION SCHEME INITIAL rhBMP-2 rhBMP-2 MFR-842 FINAL rhBMP-2CONCENTRATION VOLUME VOLUME CONCENTRATION (mg/mL) (mL) (mL) (mg/mL) 4.00.3 2.5 0.43

The rhBMP-2 solution is applied to a Helistat sponge (GeneticsInstitute) as follows:

1 Using sterile forceps and scissors, cut a 7.5 cm×2.0 cm strip ofHelistat off of a 7.5×10 cm (3″×4″) sponge.

2. Using a 1-cc syringe with a 22 G needle, slowly drip approximately0.8 mL of 0.43 mg/mL rhBMP-2 solution uniformly onto the Helistat sheet.

3. Using sterile forceps, loosely pack the sponge into the chamber ofthe dowel.

4. Using a 1-cc syringe with a 22-G needle, inject the remaining 0.8 mLof 0.43 mg/mL rhBMP-2 into the sponge in the dowel through the openingsof the chamber.

5. Implant immediately.

Example 5 Bone Dowel Packed rhBMP-2/HA/TCP Composition

A threaded dowel is obtained through the methods of Examples 1 and 2.

A vial containing 4.0 mg of lyphilized rhBMP-2 (Genetics Institute) isconstituted with 1 mL sterile water (Abbott Laboratories) for injectionto obtain a 4.0 mg/mL solution as follows:

1. Using a 3-cc syringe and 22 G needle, slowly inject 1.0 mL sterilewater for injection into the vial containing lyphilized rhBMP-2.

2. Gently swirl the vial until a clear solution is obtained. Do notshake.

A cylindrical block of biphasic hydroxyapatite/tricalcium phosphate(Bioland) is wetted with a 0.4 mg/mL rhBMP-2 solution. The BMP-ceramicblock is packed into the chamber of the dowel and the dowel is thenimplanted.

Example 6 Cortical Ring

A screened consenting donor is chosen as described in EXAMPLE 1 asfollows. A cortical ring is obtained as a cress-sectional slice of thediaphysis of a human long bone and then prepared using the methodsdescribed in Example 1. The ring is packed with an osteogeniccomposition as described in EXAMPLE 4 or 5.

Example 7 Spacers

A screened consenting donor is chosen as described in EXAMPLE 1. AD-shaped cervical spacer is obtained as a cross-sectional slice of adiaphysis of a long bone and then prepared using the methods ofExample 1. The exterior surfaces of the walls are formed by machiningthe slice to a D-shape. The engaging surfaces of the spacer are providedwith knurlings by a standard milling machine. A hole is then drilledthrough the anterior wall of the spacer. The hole is then tapped toengage a threaded insertion tool. The chamber of the spacer is thenpacked with an osteogenic composition as described in EXAMPLE 4 or 5.

EXPERIMENTAL II: BIOMECHANICAL TESTING Example 10 Static Testing ofThreaded Cortical Dowels under Axial Loading

Static testing was performed to assure that the dowels were able towithstand maximum physioloc loading, of at least 10,000 N, the maximumexpected lumbar load. Eighteen (18) mm outer diameter, frozen threadedcortical dowels 40 were obtained from the University of Florida TissueBank and thawed for testing with an axial test fixture 300. Four (4)samples of the threaded cortical dowel were inserted into two preparedplastic (polyacetal polymer) blocks 301,302 having matching geometrywith the threaded cortical dowels 40 as shown in FIGS. 50-52. Theplastic blocks 301,302 were attached to metallic blocks 301,302 toensure uniform loading across the dowel 40. A disc height H of 9 mm wasused for the testing. An axial load I′ was applied via a servohydraulictest machine to the blocks 301, 302, 303, 304 at a rate of 25 mm/min.until failure of the dowel 40. The load-displacement curves wererecorded.

Results

The threaded dowels yielded at an average load of 24,733 N. Thecompressive strength of the threaded cortical dowels provides for asignificant safety factor compared to both typical and maximumphysiological spinal loading as shown in FIG. 53. These values rangefrom 1000 N when standing to 10,000 N for heavy lifting. The compressivestrength of threaded cortical dowels and cortical rings exceeds that ofmost available bone materials used for interbody fusion as shown in FIG54. Overall, the threaded cortical dowels and cortical rings testeddemonstrated superior compressive strength compared to availableoptions, with the exception of the femoral ring allograft. Note that thetesting was for a single dowel. Clinically, most cases involve theplacement of dual, bilateral dowels. Therefore, the expected averagemaximum compressive load for 2 dowels would be 49,466 N, comparable tothe femoral ring allograft values. The threaded cortical dowels alsocompare favorably to artificial interbody implants as shown in FIG. 55.

Example 11 Dynamic Testing of Threaded Cortical Dowels Under AxialLoading

Dynamic testing determines the fatigue performance of the dowel undercyclic loading. Cycles to failure are determined at various load levels.Resistance to fatigue is important to the performance of spinalimplants. The implant must be able to withstand cyclic in vivo loadinguntil fusion occurs. It is estimated that the average person makes 2million strides per year (1 million gait cycles) and 125,000 significantbends per year. Therefore, the typical dynamic testing run-out value of5 million cycles simulates approximately 2 years of cyclic loading priorto fusion and ultimate complete spinal motion segment stabilization.

The fixture 300 (FIGS. 50-54) described in Example 11 for the axialstatic testing was used to apply dynamic alternating loads to variousimplants and dowels. Initial fatigue loads were determined based on themaximum static load value. Initial fatigue loads were 75%, 50% and 25%of the ultimate strength value of 24,733 N. Additional data points werethen generated to determine the five million cycle runout value.

Results

Based on the previously discussed physiologic loading values, an averageevery day loading value in expected to be a fraction of the maximumvalues and is estimated at approximately 3,200 N. This typical loadingvalue can then be used to assess the fatigue performance of the variousinterbody fusion alternatives. For the threaded cortical dowel, runoutwas achieved at a level of 30% of the maximum static load. That is, aminimum of 2 samples reached 5 million cycles at an applied load of7,420 N as shown in FIG. 56. This value is well above the averageloading value of 3200 N.

Example 12 Static and Dynamic Testing of Threaded Cortical Dowels UnderBending Loads

While compressive testing provided valuable comparative informationregarding the dynamic and static performance of the dowels, it is asimplification of the loading seen by the dowels in the clinicalsettings. In order to better simulate the loading seen clinically, aspecial flexion-extension or multi-axial cyclic test fixture 310 wasdeveloped (FIGS. 57 and 58). Dowels were tested in both static anddynamic loading situations. The specially designed fixture appliedcomplex, multi-axial loading to the dowels.

The dowels were placed into pre-tapped plastic (polyacetal polymer)blocks 311,312. The plastic blocks 311,312 are affixed to recessedpockets 313,314 in the upper 315 and lower 316 plates of the metal testfixture 318. Vertical loads L are applied to generate theflexion-extension bending moments. Cyclic compressive loads are applied,and a bending moment is generated by the 7.6 cm loading arm.

Two dowels were subject to a static load to failure in the test fixture.The maximum load value was then used to determine dynamic loadingvalues. For the fatigue testing, fully reversed loading was applied,simulating flexion-extension cycles. Cyclic testing was carried out atvalues of 40%, 30% and 20% of the maximum load value and the 5 millioncycle runout value was determined.

Results

The average static load to failure value for the threaded cortical dowelwas found to be 1,545 N. Given the 7.6 cm moment arm, this translatesinto a value of 138 N-m maximum bending load. The 5 million cycle runoutvalue was approximately 450 N. Again, given the 7.6 cm moment arm, thistranslates into a value of 40.5 N-m bending load. It is reported thatthe failure load of a lumbar motion segment in bending is 33 N-m onaverage. The maximum static load value is over 4 times higher than thisvalue, and the dynamic, multi-axial runout value is above this maximumbending load value.

Example 13 Insertion Torque Testing of Threaded Cortical Dowels

Benchtop testing was performed to study the insertion torque required toinsert the dowels and to compare these values with that of threadedinterbody fusion devices. Two (2) lumbar calf spines were used for theinsertion torque testing. Due to size constraints, an 18 mm threadedcortical dowel was inserted into the lowest two lumbar levels of eachspine. The disc spaces were dilated and the space was reamed and thentapped. A specially modified driver was used to place the dowels andmeasure the insertion torque.

Results

No damage was noted to any of the dowels upon examination afterinsertion. The average insertion torque value was found to be 0.78 N-m.The threaded cortical dowel compared favorably to known values for metalthreaded fusion devices as shown in FIG. 59.

Summary of Threaded Cortical Dowel Testing

The biomechanical testing demonstrates that the threaded cortical dowelsare well suited for interbody fusion applications. The test informationis summarized as follows:

1. The static strength of threaded cortical dowels provides for asubstantial safety factor over maximum physiologic load levels. Thedowels are stronger than alternative bone dowel constructs. Theirstrength exceeds that of the Brantigan composite PLIF cage and the RayTFC device and is comparable in strength to the SpineTech BAK.

2. The fatigue strength of the threaded cortical dowels exceeds that ofconventional Crock-type bone dowels and provides for a substantialsafety factor over typical, daily living load levels. The fatiguestrength of the dowels exceeds that of the Ray TFC device and iscomparable to the SpineTech BAK device.

3. The dowels are able to resist maximum bending loads, providing for asubstantial safety factor in satic loading and demonstrating 5 millioncycle runout at a value above the maximum expected bending loads.

4. The torque required to insert the devices is comparable with thatseen with threaded fusion cages. No damage to the threads or the doweldrive attachment were detected when inserting and revising the dowels.

Overall, the threaded cortical dowels possess the required biomechanicalproperties to facilitate interbody fusion in the lumbar spine. Theirphysical strength well exceeds the expected physiological loading and issuperior to other bone graft alternatives. The dowels outperform or arecomparable to all currently available fusion cage alternatives.

Example 14 Evaluation of rhBMP-2 as a Bone Graft Enhancing Agent

The purpose of this study was to determine the effect of using BMP toaugment allograft to fill a gap surrounding a porous coated implant. Anon-weight bearing canine model was used.

Raw Materials AMOUNT MATERIAL SOURCE/LOT # COMMENTS SUPPLIED rhBMP-2Genetics Institute 4 mg/mL 4 vials at Lot # 0214CO1 rhBMP-2 in 4 mg/viallyo. TQ Fill 5 mM sodium from MFR842 glutamate, 2.5% buffer glycine,0.5% sucrose, 0.01% Tween 80, pH 4.5 MFR842 Buffer Genetics Institute 5mM sodium 4 vials at Lot # 26256 glutamate, 2.5% 5 mL/vial glycine, 0.5%sucrose, 0.01% Tween 80, pH 4.5 Irradiated Fresh, Donor CaninesIrradiated 2.5 Approximately Frozen Canine Mrads (24-26 10-15 mLsAllograft KG's) Vitallium Porous Howmedica 5.4 mm diameter N/A CoatedPlugs Teflon Washers Howmedica I.D. 6.4 mm, N/A O.D. 10.4 mm Autogenicblood N/A N/A N/A Sterile Water for Abbott Labs WFI USP Grace 4 vials atInjection Lot # 90-544-DK 10 mL/vial

Composition and Graft Preparation

1. Allograft Preparation

a. Draw 1 mL canine blood.

b. Add 0.700 mL canine blook to a sterile 1.5 mL eppendorf tube.

c. Mark level on this tube.

d. Mark level on a second tube and discard the tube containing blood.

e. Mark level on three additional tubes.

f. Add allograft to level marked on tubes.

2. Allograft/Blood/rhBMP-2 Compositions

a. Reconstitute the rhBMP-2 using 1 mL, room temperature, sterile waterfor injection (WFI). Inject the WFI into a vial of rhBMP-2, along theinside surface of the vial. Gently swirl the vial 3-4 times. The finalconcentration is 4 mg/mL.

b. Draw 1.0 mL canine blood and place in a sterile eppendorf tube.

c. Draw 0.550 mL of blood from the tube and place into a secondeppendorf tube.

d. Add 0.050 mL blood of the reconstituted rhBMP-2 solution to the 0.550mL blood and mix gently with a siliconized pipet tip.

e. Add 0.300 mL of the blood/rhBMP-2 mixture to the eppendorf tubecontaining the allograft.

f. Stir the material gently with a sterile spatula until well mixed.

g. Let clot at room temperature for 1 hour.

3. Allograft/Blood/MFR842 Composition

a. Draw 1.0 mL canine blood and place in a sterile eppendorf tube.

b. Draw 0.550 mL of blood from the tube and place into a secondeppendorf tube.

c. Add 0.050 mL of the MFR842 Buffer to the 0.550 mL blood and mixgently with a siliconized pipet tip.

d. Add 0.300 mL of the blood/MFR842 mixture to the eppendorf tubecontaining the allograft.

e. Stir the material gently with a sterile spatula until well mixed.

f. Let clot at room temperature for 1 hour.

Surgery

Graft compositions were placed across each femoral condyle with a 2 mmcap maintained throughout the cancellous region of the condyle. Thecomposition on the left included fresh-frozen allograft and thecomposition on the right included fresh-frozen allograft plus rhBMP-2 asshown in the table below.

Scheme Canine ID Control: Bone Graft Only Treated: Time Bone + rhBMP-294-975 Right leg Left leg 14 days 94-973 Right legg Left leg 14 days94-913 Right leg Left leg 28 days 94-914 Right leg Left leg 28 days

The implanted compositions were evaluated radiographically andeffectiveness was tested using biomechanical shear testing or push-outstrength. Five mm thick sections were obtained for the push-out tests bymaking a cut 5 mm from the lateral end of the metal implant and a secondcut 5 mm from the first this cut. This resulted in three sections perbone specimen with the exception of one specimen which yielded foursections due to repositioning of the bone block. The biomechanical testswere completed using a computer-linked servohaudraulic materials tester.

Results

The surgeries were uneventful. The dogs were all full weight bearingwithin 3 days (2+/−1.15).

Presurgical radiographs of the distal femora from all animals revealednormal, mature bone structure with no radiographic pathology.Post-operative and terminal evaluation of the implantation sites wereperformed to assure the correctness of implant placement and to documentchanges around the implant site. No fractures or other surgicalcomplications were recognized on the radiographic images.

Push-out (compression) was achieved using a rate of 0.5 mm/sec. Allspecimens appeared to fail at the graft-metal interface. All of the twoweek specimens could be pushed our easily by finger-touch or by gravityalone. Push out testing does not appear to be adequate parameter forcomparison of the treated vs. un-treated groups at this time period.Specimens from the treated animals at the 4 week time period wereclearly superior to the untreated specimens as shown in the table below.

Load to Failure Values (N) Canine ID Time After Surgery Left Graft + BMPRight Graft Alone 975 2 weeks 8.71 24.43 973 2 weeks 17.45 12.22 913 4weeks 82.88 41.88 914 4 weeks 76.78 13.96

Push-out strength for the BMP-treated specimens was superior to thegraft alone specimens after four weeks, suggesting a BMP enhancement ofmechanical strength. The failure at the graft-metal interface indicatesa weak bond between the metal and bone four weeks postoperatively.

CONCLUSION

The combination of BMP with a bone graft provides superior results.Quicker fusion rates provide enhanced mechanical strength sooner. Boneis an excellent protein carrier which provides controlled release of BMPto the fusion site. When the bone graft is a threaded cortical dowel,the biomechanical superiority of the load bearing dowel is superblycombined with the enhanced fusion rates of the BMP-bone combination.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed:
 1. A hollow spinal spacer for engagement betweenvertebrae, comprising: an anterior wall having a convexly curvedanterior surface and opposite ends; a posterior wall having a flatposterior surface and opposite ends; two lateral walls, each integrallyconnected between said opposite ends of said anterior and posteriorwalls to define a chamber; and said walls comprised of bone and furtherdefining; a superior face defining a first opening, said opening incommunication with said chamber, said superior face having a superiorengaging surface; and an opposite inferior face defining a secondopening, said second opening in communication with said chamber, saidinferior face having an inferior engaging surface.
 2. The spacer ofclaim 1 wherein said bone is cortical bone obtained from the diaphysisof a long bone having a medullary canal, said chamber including aportion of the medullary canal.
 3. The spacer of claim 1, furthercomprising an effective amount of an osteogenic composition to stimulateosteogenesis, said composition disposed within said chamber.
 4. Thespacer of claim 1 wherein said osteogenic composition includes amaterial selected from the group consisting of autograft, allograft, abioceramic and a substantially pure osteogenic factor in apharmaceutically acceptable matrix.
 5. The spacer of claim 4 whereinsaid bioceramic is a biphasic calcium phosphate ceramic.
 6. The spacerof claim 4 wherein said factor includes a bone morphogenic proteinselected from the group consisting of BMP-1, BMP-2, BMP-3, BMP-4, BMP-5,BMP-6, BMP-7, BMP-8, BMP-9, BMP-10, BMP-11, BMP-12 and BMP-13, a mixturethereof and a heterodimer thereof.
 7. The spacer of claim 6 wherein saidmatrix is selected from the group consisting of calcium sulphates,polylactic acids, polyanhydrides, collagen, calcium phosphates andpolymeric acrylic esters.
 8. The spacer of claim 1 wherein said anteriorwall defines a tool engaging hole for receiving an implanting tool. 9.The spacer of claim 8 wherein said tool engaging hole is threaded forreceiving a threaded implanting tool.
 10. The spacer of claim 1 whereinat least one of said engaging surfaces are roughened.
 11. The spacer ofclaim 1 wherein at least one of said engaging surfaces includes teeth.12. The spacer of claim 1 wherein at least one of said engaging surfacesdefines a waffle pattern.
 13. The spacer of claim 1 further comprising ablade on at least one of said engaging surfaces.
 14. The spacer of claim1 wherein said wall defines a bone growth thru-hole therethrough, saidthru-hole communicating with said chamber and sized to receivemesenchymal cells.
 15. A spinal spacer, comprising a load bearing memberof cortical bone obtained from a cross-sectional slice of the diaphysisof a long bone having a medullary canal, said member having a wall, asuperior surface and an inferior surface said wall sized for engagementwithin an intervertebral space and defining a chamber, said chamberincluding a portion of the canal, at least one of said surfaces definingsurface roughenings for engaging the endplates of adjacent vertebrae.16. The spacer of claim 15, wherein said surface roughenings areselected from the group consisting of knurlings, a waffle pattern, andteeth.
 17. The spacer of claim 15, wherein said spacer further comprisesan effective amount of an osteogenic composition to stimulateosteogenesis, said composition disposed within said chamber.
 18. Thespacer of claim 17, wherein said osteogenic composition is a materialselected from the group consisting of autograft, allograft, a bioceramicand a substantially pure osteogenic factor in a pharmaceuticallyacceptable matrix.
 19. The spacer of claim 18, wherein said osteogenicfactor is a bone morphogenic protein.
 20. The spacer of claim 19,wherein said bone morphogenic protein is selected from the groupconsisting of BMP-1, BMP-2, BMP-3, BMP-4, BMP-5, BMP-6, BMP-7, BMP-8,BMP-9, BMP-10, BMP-11, BMP-12, BMP-13, mixtures thereof and heterodimersthereof.
 21. The spacer of claim 18, wherein said bioceramic is abiphasic calcium phosphate ceramic.
 22. The spacer of claim 15, whereinsaid load bearing member is a cortical ring.
 23. The spacer of claim 15,wherein said wall is cylindrical and said load bearing member has adiameter larger than the height of the intervertebral disc space. 24.The spacer of claim 17, wherein said osteogenic composition has a lengthgreater than the length of said chamber.
 25. The spacer of claim 15,wherein said spacer further comprises an effective amount of anosteogenic composition to stimulate osteogenesis, said body impregnatedwith said composition.
 26. The spacer of claim 15, wherein said spacerhas an outer surface that defines a tool engaging hole for receiving animplanting tool.
 27. The spacer of claim 26, wherein said tool-engaginghole is threaded to receive a threaded implanting tool.
 28. A spinalspacer, comprising a load bearing member of bone obtained from thediaphysis of a long bone having a medullary canal, said member having awall, a superior surface and an inferior surface, said wall sized forengagement within an intervertebral space and defining a chamber, saidchamber including a portion of the canal, at least one of said surfacesdefining surface roughenings for engaging the endplates of adjacentvertebrae, said surface roughenings selected from the group consistingof knurlings, a waffle pattern, and teeth.
 29. The spacer of claim 28,wherein said spacer further comprises an effective amount of anosteogenic composition to stimulate osteogenesis, said compositiondisposed within said chamber.
 30. The spacer of claim 29, wherein saidosteogenic composition is a material selected from the group consistingof autograft, allograft, a bioceramic and a substantially pureosteogenic factor in a pharmaceutically acceptable matrix.
 31. Thespacer of claim 30, wherein said osteogenic factor is a bone morphogenicprotein.
 32. The spacer of claim 31, wherein said bone morphogenicprotein is selected from the group consisting of BMP-1, BMP-2, BMP-3,BMP-4, BMP-5, BMP-6, BMP-7, BMP-8, BMP-9, BMP-10, BMP-11, BMP-12,BMP-13, mixtures thereof and heterodimers thereof.
 33. The spacer ofclaim 31, wherein said bioceramic is a biphasic calcium phosphateceramic.
 34. The spacer of claim 29, wherein said bone comprisescortical bone.
 35. The spacer of claim 34, wherein said load bearingmember is a cortical ring.
 36. The spacer of claim 29, wherein said wallis cylindrical and said load bearing member has a diameter larger thanthe height of the intervertebral disc space.
 37. The spacer of claim 30,wherein said osteogenic composition has a length greater than the lengthof said chamber.
 38. The spacer of claim 29, wherein said spacer furthercomprises an effective amount of an osteogenic composition to stimulateosteogenesis, said bone impregnated with said composition.
 39. Thespacer of claim 29, wherein said spacer includes a tool engaging portiondefining a tool engaging hole for receiving an implanting tool.
 40. Thespacer of claim 39, wherein said tool engaging hole is threaded toreceive a threaded implanting tool.